7 Medical Myths That Might Have Your Doctor Duped

Even many medical professionals believe these common misconceptions.

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Medical myths abound. For Aaron Carroll, a pediatrician at the Regenstrief Institute in Indianapolis, the last straw was hearing an ominous radio report that warned parents that strangers might try to poison their kids on Halloween. "There hasn't been one documented case of a stranger actually doing that," Carroll says. (He adds that the few Halloween candy poisoning cases that have occurred have involved the child's family, not strangers.) The radio story prompted Carroll and a fellow pediatrician, Rachel Vreeman of the Indiana University School of Medicine, to start looking for other common, unsubstantiated beliefs. They found numerous examples and have just published a report in the British Medical Journal naming seven common medical misconceptions and laying out the evidence for why they're not true.

We use only 10 percent of our brain. People have been spouting this "fact" since 1907, but numerous brain-imaging studies have shown that no area of the brain is completely inactive.

Drink at least eight glasses of water a day. We've all heard that we're supposed to drink before we're thirsty and that our pee should be as clear as mineral water, but most of us get plenty of water from food and other drinks. Drinking water when you're thirsty makes sense, but eight glasses is setting the bar too high for many people.

Hair and fingernails continue to grow after death. Makes for creepy fiction, yes, but actually it's the retraction of desiccating skin that makes the nails or hair of a cadaver appear to be growing. Real growth requires complex hormonal regulation, which stops at death.

Shaving hair causes it to grow back faster, darker, and coarser. No, no, and no. Newly sprouted hair looks dark because it has had minimal exposure to sun or chemicals, and it seems coarse because shaved hair lacks the finer taper seen at the ends of unshaven hair.

Reading in dim light ruins your eyesight. Dim light may force you to strain or squint your eyes, most ophthalmologists say, but it does not cause any eye damage.

Eating turkey makes you drowsy. Tryptophan, an amino acid that's linked to mood control and can cause drowsiness, is found in turkey meat. But chicken and ground beef contain similar amounts, and pork and Swiss cheese contain even more tryptophan per gram. Any large meal can induce sleepiness by decreasing blood flow to the brain.

Mobile phones are dangerous in hospitals. Not one death caused by the use of a cellphone in a hospital has ever been reported, according to Carroll and Vreeman, though equipment malfunctions occasionally have been. Research actually suggests that allowing physicians to use cellphones inside hospitals reduces the risk of medical error and injury.